(a) Field of the Invention
The present invention relates to a fuel cell system in which air is supplied to a cathode and hydrogen is supplied to an anode and the air is reacted with the hydrogen to generate electricity, and an operating method thereof.
(b) Description of the Related Art
A fuel cell uses electrochemical reaction of generally oxygen in air and hydrogen as fuel gas to generate electricity, and water is generated as a byproduct. The water that is generated in an electrode helps adjust the relative humidity (RH) of a membrane, but clogs the pores of a GDL (gas diffusion layer) or an electrode which in turn prevents air from being transferred to the electrode.
In some instances, when water is not appropriately eliminated and an excessive amount of water resides in electrodes and a channel/GDL a phenomena occurs called “flooding”. Flooding disturbs the transmission of air and hydrogen and the performance of a specific cell is suddenly deteriorated thus lowering overall performance of fuel cells.
In a stack portion of a fuel cell within a fuel cell vehicle, many unit cells are connected in series to generate a higher voltage, and if one cell is deteriorated, the performance of the fuel cell is limited by characteristics of the series connection of the unit cells. That is, if the flooding occurs, a driver can feel performance deterioration or a loss of power from the vehicle.
Generally, when the flooding phenomenon occurs in a fuel cell vehicle, the air flow is increased to eliminate/evaporate the water. However, when the air flow amount is increased, the power consumption is also increased and the membrane can become dry which can deteriorate the durability of the membrane, and therefore it is desirable to prevent the flooding beforehand so that such large amounts of air do not need to be applied. This flooding can be caused by nonuniform air supply rather than a shortage of overall air supply amount, and therefore the uniform air supply is an important factor so as to prevent localized flooding.
FIG. 1 is a schematic diagram of a fuel cell system. Referring to FIG. 1, a fuel cell system includes a fuel cell 200, the fuel cell 200 includes a cathode 130, an anode 160, and a cooling channel 180, and air is supplied to the cathode 130 through a filter 100, a muffler 105, an air compressor 110, an intercooler 115, and a humidifier 120 in that order. Foreign material/water within the line is then exhausted through an exhaust valve 135.
The hydrogen is supplied to the anode 160 through a hydrogen supply valve 150 and an ejector 155. One part of the gas including hydrogen that is exhausted from the anode 160 is recirculated to the anode 160 by a recirculation blower through a reservoir 165 and the ejector 155, and the other part thereof is exhausted to the outside through a purge valve 170 and a drain valve 175.
The coolant is supplied to the cooling channel 180 through a coolant reservoir 185, a radiator 190, and a 3-way valve 195, and the coolant that is exhausted from the cooling channel 180 is distributed to the 3-way valve 195 and the radiator 190 through a water pump 197.
In the fuel cell 200, the hydrogen that is supplied to the anode 160 chemically reacts with the air that is supplied to the cathode 130 to generate electrical energy, and heat that is generated by this reaction is exhausted to the outside through the coolant. Meanwhile, the hydrogen and air are non-uniformly supplied to the anode 160 and the cathode 130, and this non-uniformity causes a localized flooding phenomenon to deteriorate overall electricity generation stability.
Further, if the rotational speed of the blower (e.g., an air compressor) is increased to increase the air supply amount in a high power mode, the fuel cell efficiency is deteriorated and the overall durability can be reduced. Also, if hydrogen or air is non-uniformly supplied to the anode or the cathode, the localized flooding phenomenon can increase the load of the air compressor, and the durability of the stack portion can be deteriorated when the fuel cell is not operated for a long time and the fuel cell is started.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.